1. Field of the Invention
The present invention relates to a method for authentication in a communications network, especially a packet, e.g. IP (Internet Protocol), network.
2. Description of the Related Art
The strong growth in number of Internet users has been one of the most remarkable phenomena in communications in recent years. The Internet has born and has developed as an “open network”, being adapted to share information between users. Applications, such as the e-mail, the browsing of web pages, the download of files, based on Internet communications protocols such as the SMTP (Simple Mail Transfer Protocol), the FTP (File Transfer Protocol) or the HTTP (Hyper Text Transfer Protocol) are now of common knowledge and used by a continuously growing number of users. The Internet technology is being used also in contexts not open to the public, such as within corporate local area networks, for sharing information between employees, in a so-called Intranet environment. Recently, the W-LAN (Wireless Local Area Networks) technology is also born and is being developed, allowing Internet or Intranet users to connect to the network without the need of a cable, by exploiting wireless network terminal adapters and access points.
In order to connect to the network, a well known technique provides that the user gives its credentials in the form of a user-ID and a related password to an authentication server, possibly belonging to a service provider. For example, RADIUS (Remote Authentication Dial-In User Service) is a known server for remote user authentication based on a user-ID/password scheme.
Another proposed method for authentication to be performed for accessing a network, especially an IP network, is disclosed in the PCT patent application no. 00/02406, in the name of Nokia Networks OY. To allow authentication of users of IP networks in a geographically large area, the IP network's terminal uses a subscriber identity module (SIM) as used in a separate mobile communications system, whereby a response may be determined from a challenge given to the identity module as input. The IP network includes a special security server to which a message about a new user is transmitted when a subscriber attaches to the IP network. The subscriber's authentication information containing at least a challenge and a response is fetched from the said mobile communications system to the IP network and authentication is carried out based on the authentication information obtained from said mobile communications system by transmitting the said challenge through the IP network to the terminal, by generating a response from the challenge in the terminal's identity module and by comparing the response with the response received from the mobile communications system. Practically, as disclosed in the same PCT patent application, the authentication method of an existing mobile communications network, especially a GSM (Global System for Mobile communications) network, is used in an IP network.
Without entering in specific details, a typical authentication procedure used in a mobile communication network, such as a GSM network, provides that when a mobile terminal requires to join the mobile network it first sends the IMSI (International Mobile Subscriber Identifier), stored on the SIM associated to the mobile terminal, to the network. An Authentication Center (AuC) receives the IMSI number and generates a random number RAND that is inputted to an algorithm dedicated to the authentication (the so-called A3 algorithm). The algorithm is parameterized with an encryption key ki uniquely associated to the IMSI number and, applied to the random number RAND, gives as a result a so-called Signed Response SRES1. The random number RAND is also sent to the mobile terminal, specifically to the SIM associated to the mobile terminal, in order to challenge thereof the generation of a Signed Response SRES2, which is rendered possible from the fact that the SIM stores the same encryption key ki and algorithm A3. SRES2 is then sent to the AuC, that checks a matching between SRES1 and SRES2 in order to grant access in the mobile network to the mobile terminal. If the matching between SRES1 and SRES2 is not verified, the access to the mobile network is denied.
The use of the above mentioned authentication procedure for connection to a communications network different from a mobile network, such as the Internet or a corporate Intranet, improves security with respect to a procedure only requiring the provision of a user-ID and a password. For example, a service provider can be substantially assured that the credentials given from the user requiring the connection are genuine, i.e. that the user is truly one of its subscribers.
However, the Applicant observes that the use of the above mentioned authentication procedure does not guarantee the user in the same way with respect to the service provider, i.e. it does not guarantee the user that he/she is not giving his/her confidential data to a “fake” network, through a fake access point, provided by a malicious entity pretending to be the user's service provider. In particular, the Applicant observes that since the match between the Signed Response SRES1 generated at the AuC and the Signed Response SRES2 generated at the user's SIM is only made at the network side, the user has no way to verify that he/she is actually accessing its trusted network.
The Applicant further observes that such problem is of particular importance accessing networks by exploiting W-LAN technology, in that W-LAN fake access points are relatively easy to be implemented.
The Applicant has faced the problem of implementing an authentication method, particularly adapted for accessing a communications network, more particularly a packet-based (e.g. IP) network, in which a mutual identification can be guaranteed between a subscriber and a service provider in both directions.